In general, hand grinders used in industrial machines and equipments, shipbuilding, construction and various facilities are used for smoothly polishing uneven surfaces of parts produced through primary operation, particularly before a painting process, and for partially cutting the first raw materials such as pipes, hand bars, steel plates, etc.
In a hand grinder, a rotary shaft rotates at high speed by an operation of an electric motor or air pressure generated when a compressor operates, and simultaneously, a polishing disk assembled with the rotary shaft rotates, polishing a surface of the object formed of stone, metal, or the like to give a gross to the surface, or grinding or cutting any incomplete portions and unwanted edges after a process as a finishing work.
Typical mechanisms for engaging the polishing disk with the rotary shaft of the grinder has been disclosed in Korean Utility Model Laid-Open Publication No. 89-10365 and No. 96-26826. In the prior art, after the rotary shaft of a grinder body is inserted into a hole of the polishing disk, a nut fastens the rotary shaft, or a bolt is inserted into and then fixed to the rotary shaft.
However, since the polishing disk are fastened to the grinder body by means of only the nut or bolt, a clamping force between the polishing disk and the grind body may lower by friction or small vibration of the high-speed rotating polishing disk. Accordingly, a worker may feel uneasy about a possibility of accident arising from that the nut or bolt becomes loose and thus the polishing disk is separated from the grinder body in the middle of work. By way of precaution against such a possibility, the grinder with a fixed cover mounted near the polishing disk has been used at work site.
In addition, when a worn-out polishing disk is replaced after long-term use of the hand grinder, foreign substances such as polishing particles which stick to the nut or the bolt in a state of being hardened are found. Due to these substances, the bolt or nut is not tightly fastened to the rotary shaft of the grinder body and thus any accident arising from that the polishing disk is separated from the grinder body in the middle of work may occur.
Another prior art proposed to solve the problems described above has been disclosed in Korean Patent Laid-Open Publication No. 2009-0074461. In this prior art, a fixing holder is provided on the rotary shaft of the grinder body and a disk-integrated disk holder is fastened to the fixing holder by a screw to prevent the disk from being separated from the fixing holder. In addition, a brake unit mounted at the grinder body enables attachment and detachment of the disk to be more easily and rapidly performed.
However, this prior art is inconvenient in that, when replacing the used disk with new one in the middle of work, the worker must unfasten the screw fastening the used disk holder to the fixing holder and then fasten it again after replacement of the new one. Moreover, this prior art is inconvenient in that the worker must additionally drive a break unit when replacing the used disk.
Another prior art proposed to solve the problems described above has been disclosed in Korean Patent No. 0973157. In this prior art, the disk holder is easily fastened to the rotary shaft of the grinder body by an one-touch method. Accordingly, attachment and detachment of the disk holder can be rapidly performed. In addition, safety keys mounted in a stopper may prevent the disk holder from being separated from the grinder body.
However, the workers had found some drawbacks of this prior art while they had practically used products of this art at work site.
Firstly, the bolt fixing the stopper body to the grinder body may become loose, and thus the polishing disk may be separated from the grinder in the middle of work.
Secondly, since the safety keys are fixed by only ball plungers, the polishing disk may be separated from the grinder due to abrasion caused by long-term use.
Thirdly, if the grinder is used for long time, function of a plate spring for preventing vibration becomes weak, and thus vibration may occur.
Fourthly, an abrasion consumable consisting of many constituent parts becomes a factor increasing manufacture cost, and thus it may weaken price competitiveness of the product in the market.
Fifthly, if the grinder body itself has function of the stopper, the stopper of this art can't exhibit its function.